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| United States Patent |
5,246,783
|
|
Spenadel
, et al.
|
September 21, 1993
|
Electrical devices comprising polymeric insulating or semiconducting
members
Abstract
Disclosed are electrically conductive and semiconductive devices utilizing
polymers having resistance to water treeing and good dielectric
properties. The polymer comprises ethylene polymerized with at least one
C.sub.3 to C.sub.20 alpha-olefin and optionally at least one C.sub.3 to
C.sub.20 polyene. The polymer utilized has a density in the range of about
0.86 g/cm.sup.3 to about 0.96 g/cm.sup.3, a melt index in the range of
about 0.2 dg/min to about 100 dg/min, a molecular weight distribution in
the range of about 1.5 to about 30, and a composition distribution breadth
index greater than about 45 percent. For the polymer utilized, the tree
rating is generally less than about 40, the power factor is in the range
of about 0.0002 to about 0.0005, and the dielectric constant is in the
range of about 1.8 to about 2.4.
| Inventors:
|
Spenadel; Lawrence (League City, TX);
Hendewerk; Monica L. (Houston, TX);
Mehta; Aspy K. (Humble, TX)
|
| Assignee:
|
Exxon Chemical Patents Inc. (Linden, NJ)
|
| Appl. No.:
|
745479 |
| Filed:
|
August 15, 1991 |
| Current U.S. Class: |
428/461; 174/110R; 174/DIG.28; 174/DIG.31; 427/58; 428/76; 428/930; 526/943 |
| Intern'l Class: |
B32B 015/04 |
| Field of Search: |
524/114
526/129,119
502/117
428/461,457,76,930
427/58
174/110 R
|
References Cited
U.S. Patent Documents
| 4144202 | Mar., 1979 | Ashcaft et al. | 524/114.
|
| 4808561 | Feb., 1989 | Welborn, Jr. | 526/129.
|
| 4871705 | Oct., 1989 | Hoel | 502/117.
|
| 4937299 | Jun., 1990 | Ewen et al. | 526/119.
|
Primary Examiner: Herbert, Jr.; Thomas J.
Attorney, Agent or Firm: Kurtzman; Myron B., Sher; Jaimes
Claims
We claim:
1. An electrically conductive device having reduced treeing without the
need of a treeing inhibitor, said device comprising:
(a) an electrically conductive member comprising at least one electrically
conductive substrate; and
(b) at least one electrically insulating member substantially surrounding
the electrically conductive member, wherein the insulating member
comprises a polymer selected from the group consisting of ethylene
polymerized with at least one comonomer selected from the group consisting
of C.sub.3 to C.sub.20 alpha-olefins and C.sub.3 to C.sub.20 polyenes, and
wherein the polymer has a density in the range Of about 0.86 g/cm.sup.3 to
about 0.96 g/cm.sup.3, a melt index in the range of about 0.2 dg/min to
about 100 dg/min, a molecular weight distribution in the range of about
1.5 to about 30, and a composition distribution breadth index greater than
about 45 percent.
2. The device of claim 1 wherein the polymer has at least one of the
following properties selected from the group consisting of a density in
the range of about 0.865 g/cm.sup.3 to about 0.93 g/cm.sup.3, a melt index
in the range of about 1 dg/min to about 50 dg/min, a molecular weight
distribution in the range of about 1.7 to about 10, and a composition
distribution breadth index greater than about 50 percent.
3. The device of claim 1 wherein the polymer is polymerized utilizing a
metallocene catalyst system.
4. The device of claim 1 wherein the polymer comprises in the range of
about 68 mole percent to about 99 mole percent ethylene based on the moles
of monomer.
5. The device of claim 1 wherein the polymer is selected from the group
consisting of ethylene/C.sub.3 to C.sub.20 alpha-olefin copolymers and
ethylene/C.sub.3 to C.sub.20 alpha-olefin/C.sub.3 to C.sub.20 diene
terpolymers.
6. The device of claim 5 wherein the polymer selected from the group
consisting of copolymers of ethylene/butene-1, ethylene/hexene-1,
ethylene/octene-1, and ethylene/propylene and terpolymers of
ethylene/propylene/1,4-hexadiene and ethylene/butene-1/1,4-hexadiene.
7. The device of claim 1 wherein the polymer has at least one property
selected from the group consisting of a density in the range of about 0.87
g/cm.sup.3 to about 0.91 g/cm.sup.3, a melt index in the range of about 3
dg/min to about 30 dg/min, a molecular weight distribution in the range of
about 1.8 to about 3.5, and a composition distribution breadth index
greater than about 60 percent.
8. The device of claim 7 wherein the polymer comprises in the range of
about 73 mole percent to about 98 mole percent ethylene based on the moles
of monomer.
9. The device of claim 7 wherein the polymer is crosslinked with at least
one of the group consisting of crosslinking agents and radiation.
10. The device of claim 7 wherein the polymer is crosslinked with at least
dicumyl peroxide.
11. The device of claim 7 wherein the polymer is polymerized utilizing a
metallocene catalyst system.
12. The device of claim 7 wherein the insulating member comprises up to 50
weight percent filler.
13. The device of claim 8 wherein the polymer has a tree rating less than
about 25, a power factor in the range of about 0.0002 to about 0.0005, and
a dielectric constant in the range of about 1.8 to about 2.4.
14. The device of claim 13 wherein the conductive member comprises at least
one selected from the group consisting of aluminum, copper and steel.
15. An electrically conductive device having reduced treeing without the
need of a treeing inhibitor, said device comprising:
(a) an electrically conductive member comprising at least one electrically
conductive substrate; and
(b) at least one semiconductive member substantially surrounding the
electrically conductive member, wherein the semiconducting member
comprises a polymer selected from the group consisting of ethylene
polmerized with at least one comonomer selected from the group consisting
of C.sub.3 to C.sub.20 alpha-olefins and C.sub.3 to C.sub.20 polyenes, and
wherein the polymer has a density in the range of about 0.86 g/cm.sup.3 to
about 0.96 g/cm.sup.3, a melt index in the range of about 0.2 dg/min to
about 100 dg/min, a molecular weight distribution in the range of about
1.5 to about 30, and a composition distribution breadth index greater than
about 45 percent, and the semiconducting member further comprises a
conducting filler to render it semiconducting.
16. The device of claim 15 wherein the polymer is crosslinked with at least
dicumyl peroxide.
17. The device of claim 15 wherein the polymer is selected from the group
consisting of ethylene/C.sub.3 to C.sub.20 alpha-olefin copolymers and
ethylene/C.sub.3 to C.sub.20 alpha-olefin/C.sub.3 to C.sub.20 diene
terpolymers.
18. The device of claim 17 wherein the polymer is selected from the group
consisting of copolymers of ethylene/butene-1, ethylene/hexene-1,
ethylene/octene-1, and ethylene/propylene and terpolymers of
ethylene/propylene/1,4-hexadiene and ethylene/butene-1/1,4-hexadiene.
19. The device of claim 15 wherein the polymer comprises in the range of
about 75 mole percent to about 94 mole percent ethylene based on the moles
of monomer.
20. The device of claim 17 wherein the polymer has at least one property
selected from the group consisting of a density in the range of about
0.865 g/cm.sup.3 to about 0.93 g/cm.sup.3, a melt index in the range of
about 1 dg/min to about 50 dg/min, a molecular weight distribution in the
range of about 1.7 to about 10, and a composition distribution breadth
index greater than about 50 percent.
21. The device of claim 20 wherein the polymer is crosslinked with at least
one of the group consisting of crosslinking agents and radiation.
22. The device of claim 15 wherein the polymer has a density in the range
of about 0.87 g/cm.sup.3 to about 0.91 g/cm.sup.3, a melt index in the
range of about 3 dg/min to about 30 dg/min, a molecular weight
distribution in the range of about 1.8 to about 3.5, and a composition
distribution breadth index greater than about 60 percent.
23. The device of claim 22 wherein the polymer is polymerized utilizing a
metallocene catalyst system.
24. The device of claim 22 wherein the semiconducting member comprises up
to 50 weight percent carbon black filler.
25. The device of claim 24 wherein the polymer has a tree rating less than
about 15, a power factor in the range of about 0.0002 to about 0.0005, and
a dielectric constant in the range of about 1.8 to about 2.4.
26. The device of claim 25 wherein the conductive member comprises at least
one selected from the group consisting of aluminum, copper and steel.
27. A semiconductive device having reduced treeing without the need of a
treeing inhibitor, said device comprising:
(a) a semiconductive member; and
(b) an electrically insulating member substantially surrounding the
semiconductive member;
wherein at least one of the group consisting of the semiconductive member
and the electrically insulating member comprises a polymer selected from
the group consisting of ethylene polymerized with at least one comonomer
selected from the group consisting of C.sub.3 to C.sub.20 alpha-olefins
and C.sub.3 to C.sub.20 polyenes, and wherein the polymer has a density in
the range of about 0.86 g/cm.sup.3 to about 0.96 g/cm.sup.3, a melt index
in the range of about 0.2 dg/min to about 100 dg/min, a molecular weight
distribution in the range of about 1.5 to about 30, and a composition
distribution breadth index greater than about 45 percent, and wherein the
semiconducting member comprises a filler to render it semiconducting.
28. The device of claim 27 wherein the polymer is selected from the group
consisting of ethylene/C.sub.3 to C.sub.20 alpha-olefin copolymers and
ethylene/C.sub.3 to C.sub.20 alpha-olefin/C.sub.3 to C.sub.20 diene
terpolymers.
29. The device of claim 28 wherein the polymer is crosslinked with at least
one of the group consisting of crosslinking agents and radiation.
30. The device of claim 28 wherein the polymer is crosslinked with at least
dicumyl peroxide.
31. The device of claim 28 wherein the polymer has at least one property
selected from the group of properties consisting of a density in the range
of about 0.865 g/cm.sup.3 to about 0.93 g/cm.sup.3, a melt index in the
range of about 1 dg/min to about 50 dg/min, a molecular weight
distribution in the range of about 1.7 to about 10, and a composition
distribution breadth index greater than about 50 percent.
32. The device of claim 28 wherein the polymer is selected from the group
consisting of copolymers of ethylene/butene-1, ethylene/hexene-1,
ethylene/octene-1, and ethylene/propylene and terpolymers of
ethylene/propylene/1,4-hexadiene and ethylene/butene-1/1,4-hexadiene.
33. The device of claim 27 wherein the polymer has at least one property
selected from the group consisting of density in the range of about 0.87
g/cm.sup.3 to about 0.91 g/cm.sup.3, a melt index in the range of about 3
dg/min to about 30 dg/min, a molecular weight distribution in the range of
about 1.8 to about 3.5, and a composition distribution breadth index
greater than about 60 percent.
34. The device of claim 33 wherein the polymer is polymerized with a
metallocene catalyst system.
35. The device of claim 33 wherein the polymer comprises in the range of
about 73 to about 98 mole percent ethylene based on the total moles of
monomer.
36. The device of claim 33 wherein the semiconducting member comprises up
to 50 weight percent carbon black filler.
37. The device of claim 36 wherein the polymer has a tree rating less than
about 10, a power factor in the range of about 0.0002 to about 0.0005, and
a dielectric constant in the range of about 1.8 to about 2.4.
38. The device of claim 37 wherein the conductive member comprises at least
one selected from the group consisting of aluminum, copper and steel.
39. An electrically conductive device having reduced treeing without the
need of a treeing inhibitor, said device comprising:
(a) an electrically conductive member comprising at least one electrically
conductive substrate; and
(b) at least one protective layer substantially surrounding and supported
by the electrically conductive member, wherein at least one layer
comprises a polymer selected from the group consisting of ethylene
polymerized with at least one comonomer selected from the group consisting
of C.sub.3 to C.sub.20 alpha-olefins and C.sub.3 to C.sub.20 polyenes, and
the polymer has a density in the range of about 0.86 g/cm.sup.3 to about
0.96 g/cm.sup.3, a melt index in the range of about 0.2 dg/min to about
100 dg/min, a molecular weight distribution in the range of about 1.5 to
about 30, and a composition distribution breadth index greater than about
45 percent.
40. The device of claim 39 wherein the polymer is polymerized with a
metallocene catalyst system.
41. The device of claim 39 wherein the polymer comprises in the range of
about 73 to about 98 mole percent ethylene based on the total moles of
monomer.
42. The device of claim 39 wherein the polymer has at least one property
selected from the group consisting of density in the range of about 0.865
g/cm.sup.3 to about 0.93 g/cm.sup.3, a melt index in the range of about 1
dg/min to about 50 dg/min, a molecular weight distribution in the range of
about 1.7 to about 10, and a composition distribution breadth index
greater than about 50 percent.
43. The device of claim 39 wherein the polymer is selected from the group
consisting of ethylene/C.sub.3 to C.sub.20 alpha-olefin copolymers and
ethylene/C.sub.3 to C.sub.20 alpha-olefin/C.sub.3 to C.sub.20 diene
terpolymers.
44. The device of claim 43 wherein the polymer is selected from the group
consisting of copolymers of ethylene/butene-1, ethylene/hexene-1,
ethylene/octene-1, and ethylene/propylene and terpolymers of
ethylene/propylene/1,4-hexadiene and ethylene/butene-1/1,4-hexadiene.
45. The device of claim 39 wherein the polymer has at least one property
selected from the group consisting of a density in the range of about 0.87
g/cm.sup.3 to about 0.91 g/cm.sup.3, a melt index in the range of about 3
dg/min to about 30 dg/min, a molecular weight distribution in the range of
about 1.8 to about 3.5, and a composition distribution breadth index
greater than about 60 percent.
46. The device of claim 45 wherein the protective layer comprises up to 50
weight percent carbon black filler.
47. The device of claim 45 wherein the polymer has a tree rating less than
about 40, a power factor in the range of about 0.0002 to about 0.0005, and
a dielectric constant in the range of about 1.8 to about 2.4.
48. The device of claim 47 wherein the polymer is crosslinked with at least
one of the group consisting of crosslinking agents and radiation.
49. The device of claim 47 wherein the polymer is crosslinked with at least
dicumyl peroxide.
50. The device of claim 47 wherein the conductive member comprises at least
one selected from the group consisting of aluminum, copper and steel.
51. The device of claim 47 wherein the at least one protective layer
comprises a first shield layer adjacent the conductive member, an
insulation layer adjacent the first shield layer, a second shield layer
adjacent the insulation layer, and a jacket layer adjacent the second
shield layer.
52. The device of claim 47 wherein the at least one protective layer
comprises an insulation layer adjacent the conductive member and a jacket
layer adjacent the insulation layer.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to electrically conductive or semiconductive
products. In another aspect, this invention relates to electrically
conductive or semiconductive products comprising polyolefins. In yet
another aspect, this invention relates to electrically conductive or
semiconductive products comprising polyolefins having improved resistance
to the phenomenon of water treeing.
2. Description of the Related Art
Typical power cables generally comprise one or more conductors in a core
that is generally surrounded by several layers that include, a first
polymeric semiconducting shield layer, a polymeric insulating layer, a
second polymeric semiconducting shield layer, a metallic tape shield, and
a polymeric jacket.
A wide variety of polymeric materials have been utilized as electrical
insulating and semiconducting shield materials for power cables and in
other numerous applications. In order to be utilized in services or
products where long term performance is desired or required, such
polymeric materials, in addition to having suitable dielectric properties,
must also be enduring and must substantially retain their initial
properties for effective and safe performance over many years of service.
For example, polymeric insulations utilized in building wire, electrical
motor or machinery power wires, or underground power transmitting cables,
must be enduring not only for safety but also out of economic necessity
and practicality. It is easy to see the danger of a non-enduring polymeric
insulator on building electrical wire, or the impracticality of having to
replace underground transmission cables frequently because of a
non-enduring polymeric insulation.
One major type of failure that polymeric power cable insulation can
undergo, is the phenomenon known as treeing. Treeing generally progresses
through a dielectric section under electrical stress so that, if visible,
its path looks something like a tree, hence the name "treeing." Treeing
may occur and progress slowly by periodic partial discharge, it may occur
slowly in the presence of moisture without any partial discharge, or it
may occur rapidly as the result of an impulse voltage. Trees may form at
the site of a high electrical stress such as contaminants or voids in the
body of the insulation-semiconductive screen interface.
In solid organic dielectrics, treeing is the most likely mechanism of
electrical failures which do not occur catastrophically, but rather appear
to be the result of a more lengthy process. In the prior art, extending
the service life of polymeric insulation has been achieved by modifying
the polymeric materials so that either trees are initiated at higher
voltages than usual or the growth rate of trees is reduced once initiated.
The phenomenon of treeing itself can be further characterized as two
distinct phenomena known as electrical treeing and water treeing.
Electrical treeing results from internal electrical discharges which
decompose the dielectric. Although high voltage impulses can produce
electrical trees, and the presence of internal voids and contaminants is
undesirable, the damage which results from application of moderate A/C
voltages to electrode/insulation interfaces which contain imperfections is
more commercially significant. In this case, very high, localized stress
gradients can exist and with sufficient time lead to initiation and growth
of trees which may be followed by breakdown. An example of this is a high
voltage power cable or connector with a rough interface between the
conductor or conductor shield and the primary insulator. The failure
mechanism involves actual breakdown of the modular structure of the
dielectric material perhaps by electron bombardment. Much of the prior art
is concerned with the inhibition of electrical trees.
In contrast to electrical treeing which results from internal electrical
discharges which decompose the dielectric, water treeing is the
deterioration of a solid dielectric material which is simultaneously
exposed to moisture and an electric field. It is a significant factor in
determining the useful life of buried power cables. Water trees initiate
from sites of high electrical stress such as rough interfaces, protruding
conductive points, voids, or imbedded contaminants but at a lower field
than that required for electrical trees. In contrast to electrical trees,
water trees are characterized by: (a) the presence of water is essential
for their growth; (b) no partial discharge is normally detected during
their growth; (c) they can grow for years before reaching a size where
they may contribute to a breakdown; (d) although slow growing they are
initiated and grow in much lower electrical fields than those required for
the development of electrical trees.
Electrical insulation applications are generally divided into low voltage
insulation which are those less than 1K volts, medium voltage insulation
which ranges from 1K volts to 35K volts, and high voltage insulation,
which is for applications above 35K volts.
In low to medium voltage applications, electrical treeing is generally not
a pervasive problem and is far less common than water treeing, which
frequently is a problem.
For medium voltage applications, the most common polymeric insulators are
made from either polyethylene homopolymers or ethylene-propylene
elastomers, otherwise known as ethylene-propylene-rubber (EPR).
Polyethylene is generally used without a filler as an electrical insulation
material. Polyethylene has very good dielectric properties, especially
dielectric constant and power factor. The dielectric constant of
polyethylene is in the range of about 2.2 to 2.3 which is an acceptable
value. The power factor, which is a function of electrical energy
dissipated and lost, and therefore should be as low as possible, is around
0.0002, which is not only acceptable, but a very desirable value. The
mechanical properties of polyethylene are also very adequate for
utilization as medium voltage insulation.
However, polyethylenes are very prone to water treeing especially toward
the upper end of the medium voltage range.
There have been attempts in the prior art to make polyethylene based
polymers that would have long term electrical stability. For example, when
dicumyl peroxide is used as a crosslinking agent for polyethylene, the
peroxide residue functions as a tree inhibitor for some time after curing.
However, these residues are eventually lost at most temperatures of
electrical power cable service. U.S. Pat. No. 4,144,202 issued Mar. 13,
1979 to Ashcraft et al. discloses the incorporation into polyethylenes of
at least one epoxy containing organo silane as a treeing inhibitor.
However, a need still exists for a polymeric insulator having improved
treeing resistance over such silane containing polyethylenes.
Unlike polyethylene which can be utilized, the other common medium voltage
insulator, EPR must be filled with a high level of filler in order to
resist treeing. When utilized as a medium voltage insulator, EPR will
generally contain about 20 to about 50 weight percent filler, most likely,
calcined clay, and it is preferably crosslinked with peroxides. The
presence of the filler gives EPR a high resistance against propagation of
trees. EPR also has comparable mechanical properties to polyethylene.
While the fillers utilized in EPR may help prevent treeing, they
unfortunately will generally have poor dielectric properties, i.e. poor
dielectric constant and poor power factor. The dielectric constant of
filled EPR is in the range of about 2.3 to about 2.8. The power factor of
filled EPR is on the order of about 0.002 to about 0.005, which is about
an order of magnitude worse than polyethylene.
Thus, while polyethylene has good electric properties, and good mechanical
properties, it needs improvement in water tree resistance. While filled
EPR has good treeing resistance, it needs improvement in dielectric
properties.
Therefore, a need exists in the insulation art for a polymeric insulation
having good mechanical properties, good dielectric properties and good
water treeing resistance.
SUMMARY OF THE INVENTION
According to one embodiment of the present invention there is provided an
electrically conductive device comprising: (a) an electrically conductive
member comprising at least one electrically conductive substrate; and (b)
at least one electrically insulating member in proximity to the
electrically conductive member. In this embodiment the insulating member
comprises a polymer selected from the group consisting of ethylene
polymerized with at least one comonomer selected from the group consisting
of C.sub.3 to C.sub.20 alpha-olefins and C.sub.3 to C.sub.20 polyenes, and
wherein the polymer has a density in the range of about 0.86 g/cm.sup.3 to
about 0.96 g/cm.sup.3, a melt index in the range of about 0.2 dg/min to
about 100 dg/min, a molecular weight distribution in the range of about
1.5 to about 30, and a composition distribution breadth index greater that
about 45 percent.
According to another embodiment of the present invention, there is provided
an electrically conductive device comprising: (a) an electrically
conductive member comprising at least one electrically conductive
substrate; and (b) at least one semiconductive member in proximity to the
electrically conductive member. In this embodiment, the semiconducting
member comprises the above described polymer.
According to yet another embodiment of the present invention, there is
provided a semiconductive device comprising: (a) a semiconductive member;
and (b) an electrically insulating member in proximity to the
semiconductive member. In this embodiment, the semiconductive member
and/or the electrically insulating member comprise the above described
polymer.
According to still yet another embodiment of the present invention there is
provided an electrically conductive device comprising: (a) an electrically
conductive core member comprising at least one electrically conductive
substrate; and (b) at least one protective layer substantially surrounding
and supported by the core member. In this embodiment, at least one of the
protective layers comprises the above described polymer.
The polymer utilized in the jacketing, insulating or semiconducting member
has a tree rating less than about 40, preferably less than about 25. and
most preferably less than about 15, and even more preferably less than
about 10. Other properties of the polymer utilized in the present
invention include a dielectric constant in the range of about 1.8 to about
2.4, and a power factor in the range of about 0.0002 to about 0.0005.
There are a number of structural variables in polyolefins which effect the
ultimate properties of the polymer. Two of the most important are
composition distribution (CD) and molecular weight distribution.
Composition distribution refers to the distribution of comonomer between
copolymer molecules. This feature relates directly to polymer
crystallizability, optical properties, toughness and many other important
use characteristics. Molecular weight distribution plays a significant
role in melt processability as well as the level and balance of physical
properties achievable. Also important is the molecular weight (MW) of the
polymer, which determines the level of melt viscosity and the ultimately
desired physical properties of the polymer. The type and amount of
comonomer also effects the physical properties and crystallizability of
the copolymer.
The polymers utilized in the jacketing, insulating or semiconducting
members of the inventive devices of the present invention may be made by
any suitable process which allows for the proper control of the above
mentioned structural features (MW, MWD, CD, comonomer type and amount) to
yield the desired polymer with the desired electrical properties. One
suitable method is through the use of a class of highly active olefin
catalysts known as metallocenes.
Metallocenes are well known especially in the preparation of polyethylene
and copolyethylene-alpha-olefins. These catalysts, particularly those
based on group IV B transition metals, zirconium, titanium and hafnium,
show extremely high activity in ethylene polymerization. The metallocene
catalysts are also highly flexible in that, by manipulation of catalyst
composition and reaction conditions, they can be made to provide
polyolefins with controllable molecular weights from as low as about 200
(useful in applications such as lube oil additives) to about 1 million or
higher, as for example in ultra high molecular weight linear polyethylene.
At the same time, the molecular weight distribution of the polymers can be
controlled from extremely narrow (as in a polydispersity, M.sub.w
/M.sub.n, of about 2), to broad (as in a polydispersity of about 8).
Exemplary of the development of these metallocene catalysts for the
polymerization of ethylene is U.S. Pat. No. 4,937,299 to Ewen et al.
hereby incorporated by reference. Among other things, this patent teaches
that the metallocene catalyst system may include a cocatalyst such as
alumoxane, formed when water reacts with trialkyl aluminum with the
release of methane, which alumoxane complexes with the metallocene
compound to form the catalyst. However other cocatalysts may be used with
metallocenes, such as trialkylaluminum compounds; or ionizing ionic
compounds such as, tri(nbutyl)ammoniumtetra(pentafluorophenyl) boron,
which ionize the neutral metallocene compound, such ionizing compounds may
contain an active proton, or some other cation such as carbonium, which
ionizing the metallocene on contact, forming a metallocene cation
associated with (but not coordinated or only loosely coordinated to) the
remaining ion of the ionizing ionic compound. Such compounds are described
in U.S. application Ser. Nos. 008,800, now abandoned, and 133,480
(published as E.P.-A-0277044 on Aug. 3, 1988), U S. application Ser. Nos.
011,471, now abandoned, and 133,052 (published as E.P.-A-0277003 on Aug.
3, 1988), all herein incorporated by reference.
Metallocene catalysts are particularly attractive in making tailored
ultrauniform and super random specialty copolymer. For example, if a lower
density copolymer is being made with a metallocene catalyst such as very
low density polyethylene, (VLDPE), an ultrauniform and super random
copolymerization will occur, as contrasted to the polymer produced by
copolymerization using a conventional Ziegler catalyst.
In view of the ongoing need for polymeric electrical insulators and
semiconductors having good mechanical properties, good dielectric
properties and good water treeing resistance, it would be desirable to
provide products utilizing the high quality characteristics of polyolefins
prepared with metallocene catalysts.
Accordingly, the present invention particularly relates to polymeric
products utilizing polyolefins, wherein the products have good mechanical
properties, good dielectric properties and good water treeing resistance,
and are useful as electrical insulators and semiconductors.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an illustration of the test apparatus utilized to determine the
degree of treeing of the various samples that were tested.
FIG. 2 is a representation of the method for analyzing the test samples
once they have been aged in the test apparatus of FIG. 1.
FIG. 3 is an illustration of a typical power cable, and shows a
multiplicity of conducting substrates comprising the conductive core that
is substantially surrounded by several protective layers that are either
jacket, insulator or semiconductive shields layers.
FIG. 4(a) and FIG. 4(b) are cross-sectional views of typical medium voltage
and low voltage power lines respectively.
FIG. 5 is a graph of the peroxide response for various polymers.
FIG. 6 is a graph of the radiation response for various polymers.
DETAILED DESCRIPTION OF THE INVENTION
The polymer utilized in the jacketing, insulating or semiconducting members
of the devices of the present invention is selected from the group of
polymers consisting of ethylene polymerized with at least one comonomer
selected from the group consisting of C.sub.3 to C.sub.20 alpha-olefins
and C.sub.3 to C.sub.20 polyenes. The types of monomers selected in the
polymer utilized in the present invention will depend upon economics and
the desired end use of the resultant device.
The polyene utilized in the present invention is generally has in the range
of about 3 to about 20 carbon atoms. Preferably, the polyene has in the
range of about 4 to about 20 carbon atoms, most preferably in the range of
about 4 to about 15 carbon atoms. Preferably, the polyene is a diene, that
generally has in the range of about 3 to about 20 carbon atoms.
Preferably, the diene utilized in the present invention is a straight
chain, branched chain or cyclic hydrocarbon diene preferably having from
about 4 to about 20 carbon atoms, and most preferably from about 4 to
about 15 carbon atoms, and still most preferably in the range of about 6
to about 15 carbon atoms. Most preferably, the diene is a nonconjugated
diene. Examples of suitable dienes are straight chain acyclic dienes such
as: 1,3-butadiene, 1,4-hexadiene and 1,6-octadiene; branched chain acyclic
dienes such as: 5-methyl-1,4-hexadiene, 3,7-dimethyl-1,6-octadiene, 3,7
-dimethyl-1,7-octadiene and mixed isomers of dihydro myricene and
dihydroocinene; single ring alicyclic dienes such as: 1,3-cyclopentadiene,
1,4-cylcohexadiene, 1,5-cyclooctadiene and 1,5-cyclododecadiene; and
multi-ring alicyclic fused and bridged ring dienes such as:
tetrahydroindene, methyl tetrahydroindene, dicylcopentadiene,
bicyclo-(2,2,1)-hepta-2-5-diene; alkenyl, alkylidene, cycloalkenyl and
cycloalkylidene norbornenes such as 5-methylene-2morbornene (MNB),
5-propenyl-2-norbornene, 5-isopropylidene-2-norbornene,
5-(4-cyclopentenyl)-2-norbornene, 5-cyclohexylidene-2-norbornene,
5-vinyl-2-norbornene and norbornene. Of the dienes typically used to
prepare EPR's, the particularly preferred dienes are 1,4-hexadiene,
5-ethylidene-2-norbornene, 5-vinyllidene-2-norbornene,
5-methylene-2-norbornene and dicyclopentadiene. The especially preferred
dienes are 5-ethylidene-2-norbornene and 1,4-hexadiene.
Generally, the alpha-olefins suitable for use in the present invention
contain in the range of about 3 to about 20 carbon atoms. Preferably, the
alpha-olefins contain in the range of about 3 to about 16 carbon atoms,
most preferably in the range of about 3 to about 8 carbon atoms.
Illustrative non-limiting examples of such alpha-olefins are propylene,
1-butene, 1-pentene, 1-hexene, 1-octene and 1-dodecene.
Preferably, the polymers utilized in the devices of the present invention
are either ethylene/alpha-olefin copolymers or ethylene/alpha-olefin/diene
terpolymers. Illustrative non-limiting examples of suitable copoymers are
those such as ethylene/butene-1, ethylene/hexene-1, ethylene/octene-1, and
ethylene/propylene copolymers. Suitable examples of terpolymers include
ethylene/propylene/1,4-hexadiene and ethylene/butene-1/1,4-hexadiene.
The polymers suitable in the present invention with desired monomer levels
can be prepared by polymerization of the suitable monomers in the presence
of supported or unsupported catalysts systems. Preferably the catalyst
system utilized is a metallocene catalyst system.
The precise monomer content of the polymers utilized in the present
invention will depend upon economics and the desired applications of the
resultant device. Typically the polymers utilized in the present
invention, will generally comprise in the range of about 68 mole percent
to about 99 mole percent ethylene (based on the total moles of monomer).
Preferably, the polymers have a minimum of 73 mole percent, most
preferably, 75 mole percent ethylene. Preferably, the polymers have a
maximun of 98, most preferably, 94 mole percent ethylene. Preferably, the
polymers utilized in the jacketing, insulating or semiconducting members
of the present invention, will generally comprise in the range of about 73
mole percent to about 98 mole percent ethylene, and most preferably in the
range of about 75 mole percent to about 94 mole percent. The other
monomers will comprise the balance of the polymer.
The polymers utilized in the polymeric members of the present invention
have a density in the range of about 0.860 g/cm.sup.3 to about 0.960
g/cm.sup.3. Preferably, the polymers have a minimum density of about 0.865
g/cm.sup.3, most preferably about 0.870 g/cm.sup.3. Preferably, the
polymers have a maximum density of about 0.93 g/cm.sup.3, most preferably
about 0.91 g/cm.sup.3. Preferably the density is in the range of about
0.865 g/cm.sup.3 to about 0.93 g/cm.sup.3. Most preferably, the density is
in the range of about 0.870 g/cm.sup.3 to about 0.910 g/cm.sup.3.
Densities were measured using standard accepted procedures, except that
they were additionally conditioned by holding them for 48 hours at ambient
temperature (23.degree. C.), prior to density measurement.
The melt index (MI) of the polymers utilized in the present invention is
such that the polymer can be extruded in the desired end product.
Generally the melt index is in the range of about 0.2 dg/min to about 100
dg/min. Preferably, the MI is at least about 1 dg/min, most preferably at
least about 3 dg/min. Preferably, the maxium MI is about 50 dg/min, most
preferably about 30 dg/min. Preferably the MI is in the range of about 1
dg/min to about 50 dg/min, and most preferably in the range of about 3
dg/min to about 30 dg/min. MI as measured herein was determined according
to ASTM D-1238 (190/2.16). High load MI was determined according to ASTM
D-1238 (190/21.6).
The polymers utilized in the electrically conductive or semiconductive
devices of the present invention have a molecular weight distribution such
that the polymer will have the desired electrical properties and still be
processable into the desired end product. The ratio of M.sub.w /M.sub.n is
generally in the range of about 1.5 to about 30. The maxium ratio is
preferably about 10 and most preferably about 3.5. The minimum ratio is
about 1.5, most preferably about 1.8. Preferably the ratio is in the range
of about 1.7 to about 10, and most preferably in the range of about 1.8 to
about 3.5.
The composition distribution breadth index (CDBI) of the polymers utilized
in the polymeric members of the present invention is generally in about 45
percent or higher. Preferably, the CDBI is about 50 percent or higher.
Most preferably, the CDBI is about 60 percent or higher, and ever more
preferably, about 70 percent or higher. As used herein, the CDBI is
defined as the weight percent of the copolymer molecules having a
comonomer content within 50 percent (i.e..+-.50%) of the median total
molar comonomer content. The CDBI of linear polyethylene, which does not
contain a comonomer, is defined to be 100%.
The Composition Distribution Breadth Index (CDBI) is determined via the
technique of Temperature Rising Elution Fractionation (TREF). CDBI
determination clearly distinguishes, for example, the plastomers utilized
in this invention (narrow composition distribution as assessed by CDBI
values of about 45% or higher) from those traditionally utilized in prior
art insulation products (broad composition distribution as assessed by
CDBI values generally less than 45%). The benefits to the discovery of the
subject invention that accrue through the specific use of plastomers of
narrow composition distribution are elucidated later in the examples. The
CDBI of a copolymer is readily calculated from data obtained from
techniques known in the art, such as, for example, temperature rising
elution fractionation as described, for example, in U.S. application Ser.
No. 151,350, filed Feb. 2, 1988, now U.S. Pat. No. 5,008,204, or in Wild
et al., J. Poly. Sci. Poly. Phys. Ed., vol. 20, p. 441 (1982). Unless
otherwise indicated, terms such as "comonomer content", "average comonomer
content" and the like refer to the bulk comonomer content of the indicated
interpolymer blend, blend component or fraction on a molar basis.
By the use of a polymer as described above, a jacket, insulating or
semiconducting member can be made that will have a resistance to treeing
and good electrical properties, that is, good dielectric constant and
power factor.
The tree rating as described in the present invention is determined
according to the method of Bulinski et al., "Water Treeing in a Heavily
Oxidized Cross-linked Polyethylene Insulation", Sixth International
Symposium On High Voltage Engineering, New Orleans (Aug. 28-Sep. 1, 1989),
herein incorporated by reference. The general method is as follows. A 75
mil plaque of the material to be tested is pressed at 175.degree. C. and
then cut into 1 inch diameter circles. Three small areas are sandblasted
onto the surface of the circles to accelerate tree initiation. The samples
were stressed for 3,500 hours at 6 kV, 1000 HZ at 75.degree. C., in
contact with 0.05 M CuSO.sub.4 solution, using an apparatus as shown in
FIG. 1. The degree of treeing was determined by slicing the sample
vertically through two of the sandblasted areas and then measuring the
length of the trees relative to the thickness of the sample (stress is
proportional to the thickness). FIG. 2 is a representation of the method
for analyzing the tree retardancy test samples.
The polymer utilized in the jacketing, insulating or semiconducting member
has a good tree rating superior to that of neat polyethylenes, and that
compares well to filled EPR's. The tree rating is generally less than
about 40, preferably less than about 25, and most preferably less than
about 15, and still even more preferably less than about 10.
Not only do the polymers utilized in the present invention have good
resistance to treeing that compares favorably to filled EPR's, they also
posses good dielectric properties that compare favorably to neat
polyethylenes. Generally the dielectric constant of the polymers utilized
in the present invention is in the range of about 1.8 to about 2.4.
Another good dielectric property possessed by the polymers utilized in the
present invention is a good power factor. The power factor of the polymer
is generally in the range of about 0.0002 to about 0.0005.
The polymers useful in fabricating the jacket, insulating or semiconducting
members of the present invention may be produced by any suitable method
that will yield a polymer having the required properties, that when
fabricated into the jacket, insulating or semiconducting members of the
present invention will have suitable resistance to treeing and good
electrical properties. An illustrative nonlimiting example of a
particularly suitable method of making the polymer useful in the present
invention utilizes a class of highly active olefin catalysts known as
metallocenes, which are well known especially in the preparation of
polyethylene and copolyethylene-alpha-olefins. These catalysts,
particularly those based on group IV B transition metals, zirconium,
titanium and hafnium, show extremely high activity in ethylene
polymerization. The metallocene catalysts are also highly flexible in
that, by manipulation of catalyst composition and reaction conditions,
they can be made to provide polyolefins with controllable molecular
weights from as low as about 200 (useful in applications such as lube oil
additives) to about 1 million or higher, as for example in ultra high
molecular weight linear polyethylene. At the same time, the molecular
weight distribution of the polymers can be controlled from extremely
narrow (as in a polydispersity, M.sub.w /M.sub.n of about 2), to broad (as
in a polydispersity of about 8).
Exemplary of the development of these metallocene catalysts for the
polymerization of ethylene are U.S. Pat. No. 4,937,299 to Ewen et al.,
U.S. Pat. No. 4,808,561 to Welborn, and U.S. Pat. No. 4,814,310 to Chang,
all hereby incorporated by reference. Among other things, Ewen et al.
teaches that the structure of the metallocene catalyst includes an
alumoxane, formed when water reacts with trialkyl aluminum with the
release of methane, which alumoxane complexes with the metallocene
compound to form the catalyst. Welborn teaches a method of polymerization
of ethylene with alpha-olefins and/or diolefins. Chang teaches a method of
making a metallocene alumoxane catalyst system utilizing the absorbed
water in a silica gel catalyst support.
Specific methods for making ethylene/alpha-olefin copolymers, and
ethylene/alpha-olefin/diene terpolymers are taught in U.S. Pat. No.
4,871,705 to Hoel, and in U.S. application Ser. No. 207,672, filed Jun.
16, 1988 by Floyd et al, now abandoned, (published a E.P.-A-0347129 on
Dec. 20, 1989), respectively, both hereby incorporated by reference.
Utilizing a metallocene catalyst, the polymers useful in the present
invention can be produced in accordance with any suitable polymerization
process, including a slurry polymerization, gas phase polymerization, and
high pressure polymerization process.
A slurry polymerization process generally uses super-atmospheric pressures
and temperatures in the range of 40.degree.-100.degree. C. In a slurry
polymerization, a suspension of solid, particulate polymer is formed in a
liquid polymerization medium to which ethylene and comonomers and often
hydrogen along with catalyst are added. The liquid employed in the
polymerization medium can be an alkane, cycloalkane, or an aromatic
hydrocarbon such as toluene, ethylbenzene or xylene. The medium employed
should be liquid under the conditions of polymerization and relatively
inert. Preferably, hexane or toluene is employed.
Preferably, the polymer utilized in the insulating or semiconducting
components of the present invention is formed by gas-phase polymerization.
A gas-phase process utilizes super-atmospheric pressure and temperatures
in the range of about 50.degree.-120.degree. C. Gas phase polymerization
can be performed in a stirred or fluidized bed of catalyst and product
particles in a pressure vessel adapted to permit the separation of product
particles from unreacted gases. Thermostated ethylene, comonomer, hydrogen
and an inert diluent gas such as nitrogen can be introduced or
recirculated so as to maintain the particles at a temperature of
50.degree. C.-120.degree. C. Triethylaluminum may be added as needed as a
scavenger of water, oxygen, and other adventitious impurities. Polymer
product can be withdrawn continuously or semi-continuously at a rate such
as to maintain a constant product inventory in the reactor. After
polymerization and deactivation of the catalyst, the product polymer can
be recovered by any suitable means. In commercial practice, the polymer
product can be recovered directly from the gas phase reactor, freed of
residual monomer with a nitrogen purge, and used without further
deactivation or catalyst removal.
The polymers of the present invention may also be produced in accordance
with a high pressure process by polymerizing ethylene in combination with
the other desired monomers in the presence of the metallocene alumoxane
catalyst system. It is important in the high pressure process, that the
polymerization temperature be above about 120.degree. C. but below the
decomposition temperature of said product and that the polymerization
pressure be above about 500 bar (kg/cm.sup.2). In those situations wherein
the molecular weight of the polymer product that would be produced at a
given set of operating conditions is higher than desired, any of the
techniques known in the art for control of molecular weight, such as the
use of hydrogen or reactor temperature, may be used to make the polymer
useful in the devices of the present invention.
The polymers utilized in the present may be crosslinked chemically or with
radiation. A suitable crosslinking agent is dicumyl peroxide.
The insulating member of the device of the present invention may comprise a
"neat" polymer, or it may optionally be filled. An illustrative example of
a suitable filler is Kaolin clay. The semiconducting member of the present
invention must be filled with a conducting filler to render the member
semiconducting. The most common filler for semiconducting applications is
carbon black, which will generally comprise 30 to 40 weight percent of the
filled semiconducting member.
If filled, the products of the present invention should not be filled past
that level that would cause undue degradation of the electrical and/or
mechanical properties of the polymer. Generally, for that reason, the
filled member should comprise no more than about 50 weight percent filler,
based on the total weight of the filled member, and preferably no more
than about 35 weight percent filler.
Other additives commonly employed in polyolefin compositions such as, for
example, cross-linking agents, antioxidants, processing aids, pigments,
dyes, colorants, metal deactivators, oil extenders, stabilizers, and
lubricants may be utilized in the present invention.
The device of the present invention may take on any form that is suitable
for the use to which it will serve. The components of the devices of the
present invention, i.e. The insulating, semiconducting, and conducting
members, can be arranged relative to each other in a wide variety of ways,
depending upon the desired use of the device. Generally, the insulating
member must be arranged so that it will function as an insulator of the
conducting or semiconducting member. For example, the various components
may be: affixed together, in proxity to each other, in contact with each
other, adjacent to each other, or one may substantially surround another.
Generally in the power cable field, the device will comprise a conducting
core of one or more electrically conducting substrates that is
substantially surrounded by one or more layers of insulators and/or
semiconductor shields. FIG. 3 is an illustration of a typical power cable,
which shows a multiplicity of conducting substrates comprising the
conductive core that is substantially surrounded by several protective
layers that are either jackets, insulators or semiconductive shields. FIG.
4(a) is a cross-sectional view of a typical medium voltage power cable,
showing a conductor core comprising a multiplicity of conducting
substrates, a first semiconducting shield layer, an insulation layer, a
second semiconducting shield layer, and a jacket. FIG. 4(b) is a
cross-sectional view of a typical low voltage power cable showing a
conductor substantially surrounded by insulation and jacket layers. While
the present invention is of greatest advantage in low and medium voltage
applications where water treeing is most common, it is also useful in high
voltage applications.
Traditionally, the jacketing materials normally employed in power cables
comprise neoprene over EPR insulated cables, and polyvinyl chloride (PVC)
over polyethylene insulated cables. According to this invention, not only
is the polymer of the present invention suitable for the insulating and
shielding layers, it may also be utilized in the jacket layer.
All of the components of the compositions utilized in the present invention
are usually blended or compounded together prior to their introduction
into an extrusion device from which they are to be extruded onto an
electrical conductor. The polymer and the other additives and fillers may
be blended together by any of the techniques used in the art to blend and
compound such mixtures to homogeneous masses. For instance, the components
may be fluxed on a variety of apparatus including multi-roll mills, screw
mills, continuous mixers, compounding extruders and Banbury mixers.
After the various components of the composition to be utilized are
uniformly admixed and blended together, they are further processed to
fabricate the devices of the present invention. Prior art methods for
fabricating polymer insulated cable and wire are well known, and
fabrication of the device of the present invention may generally be
accomplished any of the various extrusion methods.
In a typical extrusion method, an optionally heated conducting core to be
coated is pulled through a heated extrusion die, generally a cross-head
die, in which a layer of melted polymer is applied to the conducting core.
Upon exiting the die, the conducting core with the applied polymer layer
is passed through a cooling section, generally an elongated cooling bath,
to harden. Multiple polymer layers may be applied by consecutive extrusion
steps in which an additional layer is added in each step, or with the
proper type of die, multiple polymer layers may be applied simultaneously.
The conductor of the present invention may generally comprise any suitable
electrically conducting material, although generally electrically
conducting metals are utilized. Preferably, the metals utilized are copper
or aluminum. In power transmission, aluminum conductor/steel reinforcement
(ACSR) cable, aluminum conductor/aluminum reinforcement (ACAR) cable, or
aluminum cable is generally preferred.
EXAMPLES
The ethylene/.alpha.-olefin copolymers suitable for use in the present
invention may be prepared as shown in Example I. The diolefin containing
terpolymer utilized in the present invention may be prepared as shown in
Examples II and III.
EXAMPLE I
Preparation of ethylene/.alpha.-olefin copolymers
A catalyst is prepared by adding 5.1 liters of a 10% solution of
trimethylaluminum in heptane into a dry and oxygen-free two-gallon reactor
equipped with a mechanical stirrer. 800 g of undehydrated silica gel,
containing 12.3% water, is then added into the reactor. After the addition
is complete, the mixture is stirred at ambient temperature for one hour.
20 g of di-(n-butylcyclopentadienyl) zirconium dichloride slurried in 30 l
of heptane is then added into the reactor and the mixture is allowed to
react at ambient temperature for 30 minutes. The reactor is then heated to
65.degree. C., while a nitrogen gas is purged through the reactor to
remove the solvent. The nitrogen purging is stopped when the mixture in
the reactor turns into a free-flowing powder.
The polymerization was conducted in a 16-inch diameter fluidized gas phase
reactor. Ethylene, butene-1 and nitrogen were fed continuously into the
reactor to maintain a constant production rate. Product was periodically
removed from the reactor to maintain the desired bed weight. The
polymerization conditions are shown in Table I below.
TABLE I
______________________________________
Gas Phase Polymerization
A B C
______________________________________
Temperature (.degree.F.)
121 110 145
Total Pressure (psia)
300 300 300
Gas Velocity (ft/sec)
1.55 1.85 1.70
Catalyst Feed Rate (g/hr)
3.0 3.5 8.9
Butene-1 Feed Rate (lb/hr)
5.8 6.0 5.8
Production Rate (lb/hr)
33 33 28
______________________________________
The polymerized products "A", "B" and "C" are useful for use in the present
invention and had characterizing properties as shown in Table II below:
TABLE II
______________________________________
Characterization Data
A B C
______________________________________
Melt Index (dg/min)
3.3 9.5 9.0
Density (g/cm.sup.3)
0.882 0.88 0.895
M.sub.n 41380 27910 31450
M.sub.w 78030 58590 62670
M.sub.w M.sub.n
1.89 2.10 1.99
______________________________________
Note:
M.sub.n is number average molecular weight.
M.sub.w is weight average molecular weight.
Both determined via the technique of Gel Permeation Chromatography, a wel
accepted procedure.
It will be recognized by persons skilled in the art, that products with
different Melt Indices and Densities to A, B, and C above can be obtained
by changing the process conditions. Additionally, the composition of the
products can be altered, depending on the choice of alpha-olefin comonomer
used.
EXAMPLE II
Preparation of diolefin-containing copolymers
A catalyst is prepared by adding 2.7 liters of a 10% solution of
methylalumoxane (MAO) in toluene into a dry and oxygen-free two-gallon
reactor equipped with a mechanical stirrer. 800 g of silica gel, dried at
800.degree. C. is slowly added into the reactor. After the addition is
complete, the mixture is stirred at 65.degree. C. for one hour. 20 g of
bis-indenyl zirconium dichloride dissolved in 30 l of toluene is then
added into the reactor and the mixture is allowed to react at 65.degree.
C. for 30 minutes. Nitrogen gas is then purged through the reactor to
remove the solvent. The nitrogen purging is stopped when the mixture in
the reactor turns into a free-flowing powder.
The polymerization was conducted in a 16-inch diameter fluidized gas phase
reactor. Ethylene, 1-4 hexadiene, butene-1 and nitrogen were fed
continuously into the reactor to maintain a constant production rate.
Product was periodically removed from the reactor to maintain the desired
bed weight. The polymerization conditions are shown in Table III below.
TABLE III
______________________________________
Gas Phase Polymerization
D E
______________________________________
Temperature (.degree.F.)
136 136
Total Pressure (psia) 300 300
Gas Velocity (ft/sec) 1.86 1.85
Catalyst Feed Rate (g/hr)
15 15
Butene-1 Feed Rate (lb/hr)
5.5 4.8
1-4 Hexadiene Feed Rate (lb/hr)
0.7 0.5
Production Rate (lb/hr)
19 15
______________________________________
Polymerized product D had a Melt Index of 6, a density of 0.893 g/cm.sup.3
and a 2.1 mole % level of incorporated 1-4 hexadiene. Polymerized product
E had a Melt Index of 5.5, a density of 0.897 g/cm.sup.3 and a 1.3 mole %
level of incorporated 1,4 hexadiene.
It will be recognized by persons skilled in the art that products with
different Melt Indices, Densities and levels of incorporated 1,4 hexadiene
to D and E above, can be obtained by changing the process conditions.
Additionally, the composition of the products can be altered, depending on
the choice of alpha olefin comonomer used.
EXAMPLE III
Preparation of diolefin-containing copolymer
A catalyst is prepared by adding 5.1 liters of a 10% solution of
trimethylaluminum in heptane into a dry and oxygen-free two-gallon reactor
equipped with a mechanical stirrer. 800 g of undehydrated silica gel,
containing 12.3% water, is slowly added into the reactor. After the
addition is complete, the mixture is stirred at ambient temperature for
one hour. 20 g os bis-indenyl zirconium dichloride slurried in 30 l of
heptane is then added into the reactor and the mixture is allowed to react
at ambient temperature for 30 minutes. The reactor is then heated to
65.degree. C., while the nitrogen gas is purged through the reactor to
remove the solvent. The nitrogen purging is stopped when the mixture in
the reactor turns into a free-flowing powder.
The polymerization was conducted in a 16-inch diameter fluidized gas phase
reactor. Ethylene, 1-4 hexadiene, butene-1 and nitrogen were fed
continuously into the reactor to maintain a constant production rate.
Product was periodically removed fron the reactor to maintain the desired
bed weight. The polymerization conditions are shown in Table IV below.
TABLE IV
______________________________________
Gas Phase Polymerization
F
______________________________________
Temperature (.degree.F.)
117
Total Pressure (psia) 300
Gas Velocity (ft/sec) 1.81
Catalyst Feed Rate (g/hr)
14.5
Butene-1 Feed Rate (lb/hr)
3.4
104 Hexadiene Feed Rate (lb/hr)
0.65
Production Rage (lb/hr)
11
______________________________________
Polymerized product F had a Melt Index of 2.5 and a density of 0.887
g/cm.sup.3 and a 2.0 mole % level of incorporated 1-4 hexadiene. As
mentioned previously, products with different melt indices, densities and
levels of 1-4 hexadiene can be obtained by changing the process
conditions. Additionally, the composition of the products can be altered
depending on the choice of alpha olefin comonomers used.
EXAMPLE IV
In this Example, Polymer C, a polymer described as being useful in the
present invention is compared against 2 commercial LDPE homopolymers
[EXXON's LD-400 and LD-411] that are representative of the polyethylene
used to make XLPE power cable insulation. All polymers were tested
unfilled and crosslinked (via dicumyl peroxide).
It is well known to those of skill in the art that unfilled LDPE has
outstanding dielectric properties, superior to those of EP elastomers
(i.e. EPR or EPDM) whether neat or filled. The data in TABLE V shows that
POLYMER C has comparable dielectric performance to that displayed by LDPE.
TABLE V
______________________________________
Dielectric Properties (Unfilled Polymers)
______________________________________
Polymer C 100
LDPE Homopolymer 100
(2.8 MI, 0.9175D)
LDPE Homopolymer 100
(2.3 MI, 0.921D)
DICUP R 2.6 2.6 2.6
ELECTRICAL PROPERTIES
DIELECTRIC CONSTANT
+ ORIGINAL 2.30 2.37 2.37
+ 1 DAY/90C WATER 2.00 2.16 2.16
+ 7 DAYS/90C WATER 1.92 2.15 2.14
+ 14 DAYS/90C WATER 1.92 2.14 2.12
+ ORIGINAL POWER FACTOR
0.00053 0.00057 0.00056
+ 1 DAY/90C WATER 0.00060 0.00054 0.00055
+ 7 DAYS/90C WATER 0.00063 0.00056 0.00062
+ 14 DAYS/90C WATER 0.00069 9.00056 0.00064
______________________________________
EXAMPLE V
In this Example, dielectric properties were remeasured for four Superohm
3728 type formulations (at 0, 30, 60 and 100 parts filler as shown in
TABLE VI). The data in TABLE VII shows the gradual deterioration in the
dielectric performance with increasing filler loading. Commercially
available filled compounds based on EP elastomers vary in filler loading
from about 30 parts (20 wt %) to about 110 parts (47 wt %), depending on
requirements for product extrudeability, dielectric performance, tree
retardance performance, physical properties, as well as other
requirements. The polymers utilized in this invention that display
inherently good tree retardance allow compound formulation with less
filler, thereby allowing a more favorable balance of dielectric, tree
retardant and physical properties to be achieved.
TABLE VI
______________________________________
Filled Insulation Formulations
______________________________________
POLYMER: Ethylene/Butene-1 Copolymer
2.0 Melt Index
0.8971 G/CM.sup.3 Density
Similar to Polymer C, but lower Melt
Index
FORMULATIONS:
SUPEROHM 3728 Type Formulation,
But at 0, 30, 60 and 100 Parts
Filler (TRANSLINK - 37, i.e. calcined
clay) per 100 parts of Polymer
NOTE: SUPEROHM 3728 is a well regarded
filled EP-based electrical insulation
compound TRANSLINK-37 is a calcined
clay and is a widely used filler used in
filled electrical insulation compounds
______________________________________
TABLE VII
______________________________________
Dielectric Properties of Filled Insulation Formulations
(0 (30 (60 (100
Parts Parts Parts Parts
Filler)
Filler) Filler) Filler)
______________________________________
ORIGINAL
Dielectric Constant
2.281 2.488 2.631 2.836
Power Factor 0.00130 0.00245 0.00300
0.00399
Vol. Resist 38 4.9 4.7 3.0
(10.sup.15 OHM-CM)
AGED 24H WATER 90 C
Dielectric Constant
2.225 2.436 2.543 2.776
Power Factor 0.00170 0.00221 0.00262
0.00323
Vol. Rest. (10.sup.15 OHM-CM)
13 3.2 7.5 1.8
______________________________________
EXAMPLE VI
In this Example, polymers useful as insulating and semiconducting
materials, are compared against commercially available polymers.
The data show polymers of this invention provide a favorable balance of
dielectric properties, tree rating, and physical properties vis-a-vis,
unfilled crosslinked polyethylene and filled EPR.
TABLE VIII
__________________________________________________________________________
Evaluation of Insulation Formulations
1 2* 3** 4* 5 6*
Unfilled
Filled Filled Filled
Unfilled
Filled
Crosslinked
Crosslinked EP
Crosslinked EP
Crosslinked
Crosslinked
Crosslinked
LDPE I II Polymer A
Polymer F
Polymer
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D
DIELECTRIC PROPERTIES
Dielectric Strength
775 750 725 700 775 720
(V/MIL)
Dielectric Constant
Original 2.37 2.76 2.85 2.71 2.32 2.70
Aged 24 Hr/90#C Water
1.16 2.51 2.7 2.44 2.05 2.50
Power Factor
Original 0.00030
0.0021 0.004 0.0024
0.00026
.0025
Aged 24 Hr/90#C Water
.00034
0.0064 0.008 0.0063
0.00026
.0065
TREEING PERFORMANCE
Tree Retardance Rating
68 1-5 15-20 15-35 5-10 5-10
(100 .times. L/T)
PHYSICAL PROPERTIES
Tensile Strength (PSI)
Original 2300 1710 1300 2555 2475 2700
Aged 7 days (.degree.C.)
136 150 150 150 150 150
% Retained on Aging
95 100 100 100 98 98
Elongation (%)
Original 525 320 300 405 540 370
Aged 7 days (.degree.C.)
136 150 150 150 150 150
% Retained on Aging
95 94 90 92 98 90
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*Typical Superohm type formulation.
**Alternative commercial EP formulation with a minimal stabilization
package.
EXAMPLE VII
In this Example, polymers suitable for use in the present invention are
compared against various commercially available polymers for tree
retardancy. As was explained above in the Detailed Description, the tree
rating as utilized in the present invention is determined according to the
method of Bulinski et al., "Water Treeing in a Heavily Oxidized
Cross-linked Polyethylene Insulation", Sixth International Symposium On
High Voltage Engineering, New Orleans (Aug. 28-Sep. 1, 1989). The general
method is as follows. A 75 mil plaque of the material to be tested is
pressed at 175.degree. C. and then cut into 1 inch diameter circles. Three
small areas are sandblasted onto the surface of the circles to accelerate
tree initiation. The samples were stressed for 3,500 hours at 6 kV, 1000
HZ at 75.degree. C., in contact with 0.05 M CuSO.sub.4 solution, using an
apparatus as shown in FIG. 1. The degree of treeing was determined by
slicing the sample vertically through two of the sandblasted areas and
then measuring the length of the trees relative to the thickness of the
sample (stress is proportional to the thickness). FIG. 2 is a
representation of the method for analyzing the tree retardancy test
samples. Tree rating data is presented in TABLE IX below.
In TABLE IX, the polymers suitable to be utilized in this invention are
referred to by the tradename EXACT, or by the polymer designation from
Examples 1-3. The commercially available EXACT polymers are referred by
product number. Those EXACT polymers not having a product number, are
pilot plant samples.
TABLE IX
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NRC TREE RETARDANCY DATA
(Sorted by Length/Thickness (.times. 100))
Sample* L/T(.times. 100)
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32 LPDE (50)/Semicrystalline EP(50)/
0
Translink 37(25)
21 Commercial Filled MV Insulation
0
Compound
22 Commercial Filled MV Insulation
6
Compound
14 Amorphous PE 7
17 POLYMER F 8
33 LDPE (50)/Semicrystalline EP (50)/
9
Translink 37(50)
10 Commercial XLPE 9
15 Commercial P(100)/Translink 37(30)
11
9 POLYMER C 16
4 MDV 87-31 (in commercial MV EP
16
insulation formulation)
19 Commercial XLPE 16
16 Amorphous PE (100)/Translink 37(60)
16
5 Semi-crystalline EP copolymer/
16
Flexon/Translink 37(101)
31 LD180 50/Semicrystalline EP(50)
19
1 EMS 4003 (SLP .rho. = 0.895, MI = 9,
20
C.sub.2 = /C4 =)
11 Commercial LLDPE 20
6 Commercial tree retardant XLPE
22
13 Amorphous PE 25
12 EXACT (.rho. = 0.939, MI = 7,
33
C.sub.2 = /C.sub.4 =)
7 POLYMER C 33
8 POLYMER A 36
23 EXACT (.rho. = 0.884, MI = 1.7,
39
C.sub.2 = /C.sub.3 =)
3 Commercial LDPE 46
30 LDPE (60)/Semicrystalline EP (40)
46
25 EXACT (.rho. = 0.885, MI = 4,
58
C.sub.2 = /C.sub.6 =)
18 Commercial XLPE 68
27 LDPE (90)/Semicrystalline EP(10)
69
28 LD180 80/Semicrystalline EP(20)
70
24 EXP314 (.rho. = 0.886, MI = 5,
70
C.sub.2 = /C.sub.4 =)
2 POLYMER C 70
26 Commercial LDPE 98
29 LDPE (70)/Semicrystalline EP(30)
98
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*All samples were crosslinked with Dicup R and contain a minimal
stabilization package.
EXAMPLE VIII
In this Example, the crosslinkability of the polymers utilized in the
present invention are compared to commercially available polymers. The
polymers were crosslinked with both dicumyl peroxide and with radiation.
The peroxide response of the polymers of the present invention (including
diolefin-containing polymers which provide residual olefinic unsaturation)
compared to semicrystalline EPDM and a standard LDPE are shown in FIG. 5.
In this FIG. the polymers useful in this invention are designated by the
tradename "EXACT". This figure shows that in an environment of equivalent
peroxide levels, the polymers utilized in the present invention will have
a greater response, as evidenced by greater torque values.
The radiation response of the polymers of the present invention compared to
LDPE is shown in FIG. 6. In FIG. 6, the polymer useful in the present
invention is designated by the tradename "EXACT". As can be seen in FIG.
6, the polymers utilized in the present invention show a greater response
to radiation relative to LDPE as measured by levels of torque.
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